A few months ago, our guild brought in a presenter who led us through a session of chair yoga tweaked to support quilters. I'm not a big fan of yoga in general - I appreciate it, but I'm not very flexible and I don't like being upside down - but I found the session she led was really helpful and I left the meeting minus a few aches and kinks, especially in my neck and shoulders. As Three Dog Night mentioned, there are lots of good videos for stretches for the different parts that tend to stiffen up when we spend a little too much time in the quilting room.
One of the things that I do (not necessarily by choice, but it's worked out well) is I walk a lot between piecing units, simply because my ironing board is down the hall in the laundry room. :-)